The overall aim of this proposal is to enhance our knowledge of the etiology, pathophysiology and treatment of endometriosis. Endometriosis is a human disease that is characterized by the presence of benign endometrial implants that grow outside the uterus in the peritoneal cavity and it is associated with infertility, early pregnancy loss, and pelvic pain. Unfortunately, the mode of action through which ectopic endometrial implants affect the reproductive system in unclear. A rat model has been developed in order to study clinical and basic aspects of the disease which cannot be investigated adequately in the human. Endometrial tissue that is surgically implanted in the peritoneal cavity of the rat grows and functions in a fashion similar to the endometriotic implants of human endometriosis. Furthermore, endometriotic implants in the rat even induce infertility. A series of five groups of experiments using the rat model are proposed. These experiments examine the endocrine interplay between endometriotic implants and the reproductive physiology of the rat. In particular, these experiments will: a) assess the effect of the estrous cycle upon endometriotic implants, b) determine the influence that endometriotic implants have upon ovulation, conception and nidation, c) attempt to mimic the anti-fertility effects of the endometriotic implants with peritoneal infusion of prostaglandins, d) examine the effect of aging upon endometrial implants and e) study the effect of various hormones of drugs on infertility due to endometriosis.